Human beings have solid vision. It is formed by two eyes set apart in the cavities of facial bone separated by the nose. The belief that both eyes view the same field kept us making cameras with a single set of lens viewing from one point. All along the solid vision is lacking in our prints and movies.
In the last two decades the idea became prevalent that since in nature two eyes view the field from two different points to obtain solid vision, use of two cameras representing the eyes would be necessary to produce the same kind of vision. This idea gave rise to 3D pictures and 3D movies.
In this process the images are formed in pairs, by shooting the field with two still or movie cameras depicting the pair of eyes. The cameras are set parallel to each other at a distance apart. They are fitted with filters of different orientations. In case of stills, the images are printed one over the other and viewed wearing glasses, corresponding to filters used in the cameras. In the case of movies, the sets of images are printed on the same film roll, one in the upper half and the other in the lower half of the width of the film. The movie is projected on the screen magnifying both the recordings to the screen's full height and viewed wearing glasses, corresponding to filters used in the cameras. The resulting picture and the image on the screen give us a sensational feel of depth which, however, is not natural.
The background art of photography in human solid vision depended on the scientific knowledge on the subject of human vision. A concise know-how of human vision is found in a chapter called “The Eye” in the volume named “The Human Body” of the authentic “World Book Encyclopedia of Science”. The problems encountered in making a true reproduction in human solid vision can be appreciated from the questions raised on an illustration and on a sentence from the text. In the illustration of “The Visual Pathways” the axes of the eyes are shown converging on an object. If the axes of the eyes are to converge on any object would not all the other objects in the field appear double? In the last sentence of the para three it is said: “The eyes overlapping fields of view produce the binocular vision that enables us to judge depth and distance”. If the same field is viewed by the two eyes would not two images which are different from each other appear?